There are no plans to port Feathers UI to Starling for Haxe/OpenFL. The new version of Feathers UI will run directly on OpenFL, with no dependency on Starling. In theory, it can be used with Starling indirectly by adding the Feathers UI components to the OpenFL display list, but they will always be at a higher depth than the Starling content. Depending on your requirements, that may or may not matter.
An older port that runs on Starling is available here, but I cannot say how well it works. I do not maintain this port.